Looks like you were right. At 10mm the aperture doesn't seem to close properly. If I use the aperture lever to open the aperture, it remains stuck in that position. When zooming in just a little bit, the aperture blades do close just fine.

Is this something that can easily be fixed (for a reasonable price) at a service center? I have zero experience with that.

When i added the right floats to get my rig completely neutral a new way of diving with a camera opendto me.No hassle, no micro blurred pictures, 2 hands free to do something else while the camera float by my side,cool self videos with the camera floating in front of me, slower, not jerky movements while recording video, and so on ...

Never again diving with a positive or negative buoyant camera rig!

How do you manage to make the housing stay horizontal? I also have a Hugyfot housing, and with the right amount of floats I can make the housing perfectly neutral, but I'm still having trouble with the horizontal balance. The port (macro or dome) at the front is relative light (plastic) and has a large volume, while the back is heavier (metal and a 45 degree viewfinder attached). The net result is that the port will always try to flip up. So I wonder how you fixed that, because in your video, the housings stays perfectly horizontal.